The present invention relates to a dual-roll type continuous casting machine.
In a conventional dual roll type continuous casting machine as shown in FIG. 1, melt 4 is supplied to an upper space defined by two cooling rolls 2 and 3 which are disposed horizontally and in parallel with each other and which have side weirs 1 disposed on both sides of the cooling rolls 2 and 3, thereby forming a basin. The melt 4 is cooled by the cooling rolls 2 and 3 and a casting 5 is pulled out of a gap or nip between the cooling rolls 2 and 3.
Continuous casting by the above mentioned machine tends to involve a triple-point problem. More specifically, a solidified shell 7 grows integrally on cylindrical surfaces of the cooling rolls 2 and 3 and an inner surface of the side weir 1 at a triple-point 6 (i.e., the point of contact between the cooling rolls 2 and 3, the stationary side weir 1 and the melt 4) and is torn off due to rotation of the cooling rolls 2 and 3. As a result, lateral sides of the casting 5 may have defects 8 in various shapes so that the melt 4 which is still in the liquid state inside the casting 5 may flow to the exterior and the casting 5 may be broken.
Therefore, recently there has been used a system in which part of the melt 4 supplied to the basin is positively directed to the triple-point regions 6, whereby growth of the solidified shell on the side weirs 1 is prevented. Furthermore, flow rate of the melt 4 supplied to the basin is controlled in accordance with thickness of the casting 5 and the casting velocity so as to maintain constant the level H of the melt 4 in the basin.
When the flow rate of the melt 4 supplied to the triple-point region 6 is too high in the above-described system, the solidified shell on the cooling rolls 2 and 3 also melts and the lateral sides of the casting 5 have drop- or buldge-shaped run outs or defects 9. On the other hand, when the flow rate of the melt 4 supplied to the basin is too low, the above-described triple-point problem results. Variation of the flow rate of the melt supplied to the triple-point region 6 is due to variations of casting conditions such as variation in quantity of the melt in a tundish (not shown) as a supply of melt above the basin, variation in cross-sectional area of a melt supply passage due to adhesion of materials to the inner wall surface thereof and temperature variation of the melt.
Adjustment in flow rate of the melt supplied to the triple-point region 6 for overcoming the above-mentioned problems would involve variation in level H of the melt which in turn causes the displacement of the supplied position of the melt to the triple point region 6 for prevention of the triple point problem, resulting in above-mentioned defects 8 and 9 in shape.
Therefore, conventionally, adjustment for maintaining the level H of the melt is carried out without adjustment of the flow rate of the melt to the supplied triple-point region at all so that because of the above-described variations of casting conditions the lateral sides of the casting 5 may have defects 8 and 9 in shape, resulting in degradation in quality of the casting and increase of cost due to resultant difficulties of succeeding rolling or the like operations. Furthermore, with the level of the melt being maintained constant, the triple point problem still tends to frequently occur especially at the beginning of continuous casting because of reduction in cross-sectional area of the melt supply passage and consequent reduction in flow rate of the melt supplied to the basin, resulting in decrease of the yield of the casting.
The present invention was made to overcome the above and other problems encountered in the conventional dual roll type continuous casting machines and has for its object to control the flow rate of the melt supplied to the triple point regions in response to the shapes of the lateral side surfaces of the casting and to automatically maintain constant the level or height of the melt in the basin so that a high quality casting can be produced.
Now a preferred embodiment of the present invention will be described with reference to the accompanying drawings.